The object of the study was the grain of winter barley harvested at the beginning of its setting, milk maturity, dough maturity and full grain maturity stages at nitrogen fertilization doses of 0, 60, 120 and 180 kg N^.ha^-1. The experiment was carried out at the Research Station in Wierzchucinek (53^o26’ N; 17^o79’ E) owned by the University of Technology and Life Sciences, Bydgoszcz. The results of the research revealed that the contents of all the tested individual fractions in total protein generally increased during the filling of the winter barley grain. It mostly concerned prolamins, for which the difference in the contents between stage A and stage D was on average 207.7% for three years of the research. A fraction of spare proteins, i.e. prolamins and glutelins, increased significantly (by 15.7%), whereas the content of albumins and globulins decreased in the protein of ripening grain of winter barley (by 18.2%) in all the tested stages of grain growth under the effect of nitrogen fertilization (0-180 kg N·ha^-1). The highest effect of nitrogen doses on the protein fractional composition was observed in the phase of full grain maturity. Quantitative variations in proportions between protein fractions during the ontogenesis of the winter barley grain in relation to the intense nitrogen fertilization may suggest some decline in nutritional value of the protein.

The study was conducted in north-eastern Poland (53^o35′ N; 19^o51′ E), over 2000-2002. The aim of the experiment was to determine the effect of simplified tillage and different plant density per area unit on the morphometric characters and yield of faba bean cv Tim. Plant density was found to be the only factor which significantly affected first pod height, the number of pods per plant, thousand seed weight and seed yield. A correlation between temperature and moisture conditions and yield structure components was observed throughout the study period.

Research results come from a field experiment which was conducted over 2002-2004 at the Zawady Experimental Farm owned by the University of Podlasie, Siedlce (52^o06’ N; 22^o06’ E). Experimental design was a split-plot arrangement of treatments in a randomized complete block with three replications (blocks). The aim of this work was to determine an impact of soil tillage methods (conventional and simplified) as well as seven weed control methods in potato stand on dry matter, starch and total protein yields. A significant impact of weed control methods and study years on tuber dry matter yield, starch yield and total protein yield was found. The highest yields of the above-mentioned characteristics were obtained in the treatment where mechanical weed control was applied prior to potato emergence, and a mixture of herbicides Plateen 41.5 WG (2.0 kg·ha^-1) + Fusilade Forte 150 EC (2.5 dm³·ha^-1) + Atpolan 80 EC 1.5 (dm³·ha^-1) was used post-emergence. The lowest yields were recorded in the treatment where mechanical control was applied pre- and post-emergence.

A field experiment was carried out in the years 2002-2004 at the Zawady Experimental Farm owned by the University of Podlasie, Siedlce (52^o06’ N; 22^o06’ E). The factors were: two methods of soil tillage (conventional and simplified), and four methods of weed control in potato cultivation based on herbicide application. The objective was to determine economic effects of various weed control methods in potato cultivation. The economic effectiveness of the four methods of weed control in potato cultivation, for both the conventional and simplified tillage method, was conditioned by costs of weeding operations, herbicide prices, the level of yield and its value. The highest profitability of weed management was found in the treatment where mechanical and chemical control, including Plateen 41.5 WG herbicide (1.6 kg·ha^-1) + Fusilade Forte 150 EC graminicide (2.0 dm·ha^-1) + Atpolan 80 EC adjuvant (1.5 dm^3·ha^-1), was applied. The financial result was also improved by the soil tillage methods. The simplified soil tillage was more effective from the economic standpoint.

The aim of this research was to obtain the influence of fertilization level and sowing density on changes in the grain yield of the winter triticale cv. Woltario. The experiment was conducted in micro plots (m²) at the Institute of Soil Science and Plant Cultivation – State Research Institute (PIB) in Puławy, Poland (51^o25’ N; 21^o58’ E) over 1999-2002. The factors were: NPK fertilization level: 160, 260 and 360 kg·ha^-1 and sowing density (100, 200, 300 grains·m^-2). It was found that the biggest grain yield was obtained under a density of 200 plants^.m^-2 and a fertilization level of 260 kg NPK·ha^-1. Further increase in plant density and nitrogen fertilization did not influence yield level. Variability of the grain yield depending on the studied factors was related mainly to differentiation in the number of ears per area unit.

The experiment was conducted at the Research and Didactic Station of Poznań University of Natural Sciences (52^o29' N; 16^o49' E). The aim of the research was to evaluate the effect of tillage systems: ploughing system (traditional), no-ploughing system (reduced) and zero system (direct sowing), foliar microelement fertilization (Mikrosol, Ekolist and Wuxal) and harvest methods (two-stage – of entire plants and pods only, one-stage – manual and with a combine harvester) on the quality of seeds of the yellow lupine variety Parys. The seed vigor was determined with the conductivity test, seedling growth test and seedling evaluation test. Additionally, the vigor index and seedling length sum were calculated. The tillage systems and foliar fertilizers applied did not affect the germination capacity and vigor determined by the conductivity test and vigor growth tests. Yellow lupine seeds from two-stage harvest of entire plants and one-stage harvest with a combine harvester were characterized by the highest germination capacity. Seeds harvested with a combine harvester or the seeds from two-stage harvest of entire plants also obtained the highest parameters in vigor tests. Seeds coming from no-ploughing tillage system, after two-stage harvest of entire plants or combine harvest were characterized by the highest vigor.

During a pot experiment run at the greenhouse laboratory of University of Warmia and Mazury in Olsztyn (53^o46'26" N; 20^o29'30" E) in three series over 2002- -2005 on light and heavy soils, the process of competition between spring barley and field peas was investigated for three periods determined by the development rhythm of barley as single crop, i.e. during the stages of: seedling growth (Zadoks 10-13), tillering (25), stem elongation (32), heading (55) and ripening (87-91). The experiment was established according to the additive pattern in 4 repetitions. During the determined periods the yields of dry mass from different parts of plants (stems, leaves, heads, hulls and roots) were determined. The data was used for computation of crop growth rate. It was shown that joint cultivation of both species, as compared to single crop cultivation, from the very beginning of vegetation led to reduction of their overground and root mass. The process intensified with the passage of time. The negative influence of the added component was less limiting for the dry mass increase in stems but it was the most pronounced in the heads and hulls. The type of soil base had no influence on the accumulation of dry mass in the plants of spring barley and in the overground parts of field pea as opposed to its roots where a larger reduction in roots biomass was recorded in heavy soil. In case of mixture crop, the biomass accumulation rate decrease was recorded for both species over the entire vegetation period.

During a pot experiment run in three series over 2002-2005 on light and heavy soils, the process of competition between spring barley and field peas was investigated for three periods determined by the development rhythm of barley as a single crop, i.e. during the stages of: seedling growth (Zadoks 10-13), tillering (25), stem elongation (32), heading (55) and ripening (87-91). Dry mass yield of both species (overground parts and roots) was used for computation of relative yields (RY), relative yield total (RYT), and competition ratio (CR). It was found that the competence between barley and peas on light soil began during the stage of seedling growth and on heavy soil during the tillering of barley. Its intensity increased until heading on heavy soil, and until the end of vegetation period on light soil. On light soil barley predominated over peas during seedling growth, and peas predominated over barley during stem elongation and heading. The interactions were balanced in the other periods of joint vegetation. On heavy soil barley predominated over peas during seedling growth and heading, while peas predominated over barley at stages of barley tillering and stem elongation. At the ripening stage both species interacted similarly. More intense interactions between the plants were recorded on heavy soil.

A field experiment was conducted over 2004-2006. The experiment was established at the Experimental Station in Tomaszkowo, the Warmia and Mazury Province (53^o42' N; 20^o26' E). The aim of this study was to compare Festulolium and Festuca pratensis L. grown in mixtures with Lotus corniculatus L. with respect to gas exchange parameters, chlorophyll content of leaves and yield, depending on multiple nitrogen rates. It was found that under conditions of temporary water stress the rate of photosynthesis was higher for Festulolium, while under adequate moisture conditions – for Festuca pratensis L. Over the three-year experimental period Festuca pratensis L. was characterized by a significantly higher rate of transpiration and substantially higher leaf greenness values than Festulolium. Under optimum growth conditions water use efficiency was higher in Festuca pratensis L., whereas under water deficit conditions – in Festulolium. Mixtures composed of the tested grass species did not differ significantly with respect to dry matter yield. Mineral nitrogen fertilization increased the rate of photosynthesis and the yield of the investigated grass mixtures only under favorable weather conditions; under rainfall deficiency conditions the above parameters were considerably affected by the presence of Lotus corniculatus L. in the sward. Nitrogen fertilizers enabled to limit transpiration as well as to increase water use efficiency in grasses and the chlorophyll content of leaves.

The field experiment was conducted at the Agriculture Research Station Zawady (52^o20’ N; 22^o 30’ E) owned by the Podlasie Academy in Siedlce. This work presents results from the years 1999-2003 and 2007, in which harvests, value of production, direct manufacturing costs, direct surplus of winter triticale were compared. This winter triticale was planted in the second year after the application of catch crop, straw and catch crop with straw. The first factor of experiment is the presence and kind of catch crop: control object, birdsfood trefoil, birdsfood trefoil + Italian ryegrass, white mustard, white mustard – mulch. The second one is the presence of straw: without straw, with straw. Table potatoes were cultivated in the first year after application of catch crop and straw, and winter triticale in the second year. The best productive and economic result was obtained using winter triticale cultivated in the second year after mixture of birdsfoot trefoil with Italian ryegrass in combination with straw.

The field research was carried out in the years 2000-2003 at the Experimental Farm of Lublin Agricultural University, located in Bezek near Chełm (51^o19’ N; 23^o26’ E). The purpose of this work was to determine the influence of the number and dry matter of weeds on potato tuber yield and its structure with organic and mineral + organic fertilization applied in comparison with the control without fertilization, depending on the soil agronomical category. The results indicated significant negative relationships between weedness indicators (the number and mass of weeds) and potato tuber yield. The total yield of potato tubers on heavy soil was also significantly negatively correlated with the number of monocotyledonous weeds at both times of weedness observation. On light soil these relationships occurred only prior to row closing. Air-dry matter of weeds and the total number of weeds induced the increase in yield of the smallest tubers at the cost of the yield of the most valuable fractions (from 50 to 60 and more than 60 mm).

Field experiments were made over 2002-2004 at the Experimental Station of the University of Technology and Life Sciences in Mochełek (53o13’ N; 17o51’ E) on very good rye complex soil. The aim of the research was to define the effect of nitrogen fertilization of non-papilionaceous plants grown in stubble intercrop on the qualitative characters of green matter determining its applicability for cattle nutrition. Nitrogen fertilization increased the content of N-NO3 in the dry overground matter of tansy phacelia, sunflower and oilseed radish; however, even the application of 90 kg·ha-1 N did not result in exceeding its permissible concentration in cattle feed. Increasing the nitrogen dose did not result in significant changes in the content of crude fibre, potassium, calcium and magnesium in the dry overground matter of plants. The plants researched contained the amount of crude fibre, phosphorus, calcium and magnesium in the dry overground matter adequate for the purpose of animal feed, but an excessively high content of potassium.